DESCRIPTION: Angiogenesis is required for proper development of the embryonic circulatory system and is an important step in the progression of many eye diseases, including retinopathy of prematurity (ROP). Therefore, understanding how the normal regulatory systems in the endothelium keep angiogenesis in check has great clinical implications. Platelet endothelial cell adhesion molecule-1 (PECAM-1) is an important regulator of angiogenesis. We have shown that multiple isoforms of PECAM-1 are expressed in vascular beds of different tissues in a developmentally regulated fashion. The ability of these isoforms to differentially activate intracellular signaling pathways suggests specific roles for these isoforms during vascular development and angiogenesis. However, the physiological role PECAM-1 and its isoforms play in these processes requires further investigation. The main objective of this proposal is to delineate the physiological role of PECAM-1 and its isoforms in retinal vascular development and angiogenesis, as well as in regulation of retinal EC adhesive and migratory properties, and to elucidate the function of genes whose endothelium expression is differentially regulated by PECAM-1. Specifically, we will demonstrate the role of PECAM-1 in the development of retinal vasculature and neovascularization and determine how these processes are affected in the absence of PECAM-1. We will determine the expression pattern of PECAM-1 isoforms during retinal vascular development and neovascularization, as well as in retinal endothelial cells (EC). We will evaluate the specific roles of PECAM-1 isoforms in the regulation of EC adhesion and migration. To further elucidate PECAM-1's mechanism of action, we will identify and perform functional studies of genes such as endoglin and connective tissue growth factor whose endothelium-specific expression is differentially affected by the lack of PECAM-1. These studies will provide insight into the physiological role of PECAM-1 in retinal vascular development and angiogenesis and in modulation of EC adhesion and migration. This knowledge will be instrumental in the development of new treatment modalities for a variety of eye diseases with a neovascular component.